This TS defines stage 3 for the HTTP Digest AKA (RFC 3310) based implementation of Ub interface (UE-BSF),
the Disposable-Ks model based implementation of Upa interface (NAF-UE) and the HTTP Digest (RFC 2617) and the PSK TLS
based implementation of bootstrapped security association usage over Ua interface (UE-NAF) in Generic
Authentication Architecture (GAA) as specified in TS 33.220.

The purpose of the Ub interface is to create a security association between UE and BSF for further usage in GAA applications. The purpose of the Upa interface is to provide a push mechanism to created a bootstrapped security association between the UE and NAF for secure communication of pushed messages. The purpose of the Ua interface is to use the so created bootstrapped security association between UE and NAF for secure communication.